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    I wanted to find out how well my furnace/AC was working, and if I could monitor the temperature differential's between the input and output ducts. I also wondered if I would be able to calculate the amount of energy being consumed by measuring the work being done. And I wanted to try something new.

    I tried several different methods, each with it's own set of problems:

  • Temperature sensitive resistor (aka a thermistor) connected to the joystick port on a PC.  The problems with this are that you need to calibrate each thermistor to each gameport.  I do not have an accurate way of doing this. It is also susceptible to wiring changes, since any change in the wire (i.e.: if the length changes, or the temperature changes, it will change the profile of the sensor).
  • Using a RC circuit on a serial/parallel port, and timing the length of time it takes trigger a logic change.  Again, the problem with this is calibrating it. It would be different for every serial port, resistor and capacitor; it would also be susceptible to wiring changes (even repositioning the wire could change the capacitance of the circuit).

    I was running out of ideas, when I came across a slashdot story about brewing beer using a computer to control the temperature.  This device seemed like it would serve my purposes, and even had a Canadian retailer.

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